The present invention relates to a method of manufacturing an organic electroluminescent device and an organic electroluminescent device.
In recent years, an organic electroluminescent device (hereinafter, referred to as an organic EL device) having a light-emitting functional layer has been known. Such an organic EL device generally has the configuration in which an organic light-emitting layer is provided between an inorganic anode and an inorganic cathode. In addition, in order to enhance hole-injection property or electron-injection property, the configuration in which an organic hole-injecting layer is disposed between the inorganic anode and the organic light-emitting layer or the configuration in which an electron-injecting layer is disposed between the organic light-emitting layer and the inorganic cathode has been suggested.
Here, the electron-injecting layer having material property ready to emit electrons is liable to react with moisture in air. With the reaction with water, the electron injection effect of the electron-injecting layer is degraded, and thus a non-light-emitting portion, which is called a dark spot, is formed, and lifetime of a light-emitting element is decreased. Accordingly, in a field of such an organic EL device, durability against moisture or oxygen needs to be enhanced.
In order to solve this problem, a method has been generally used in which a cover made of glass or a metal is attached to a substrate of a display device so as to seal against moisture or the like. However, as a display has a large screen and is reduced in size and weight, in order to hold the strength against external stress, the change from a hollow structure to a solid structure is demanded. Further, as the display becomes large, in order to ensure sufficient areas for TFTs or wiring circuits, a top emission structure, in which light is emitted from an opposite side to a circuit board, has been suggested. In order to meet such a demand, as a sealing structure, a thin structure, which is transparent and light-weight and has excellent strength, needs to be used. Further, even when a desiccant agent is removed, a structure capable of obtaining moisture-proof performance is demanded.
In recent years, in order to meet a display device, which has a large screen and is reduced in weight and thickness, a technology has been used in which a transparent thin film made of silicon nitride, silicon oxide, ceramics, or the like having excellent gas barrier property is film-deposited on the light-emitting element by use of a high-density plasma film-deposition method (for example, ion plating, ECR plasma sputter, ECR plasma CVD, surface acoustic wave plasma CVD, ICP-CVD, or the like) (for example, JP-A-9-185994, JP-A-2001-284041, JP-A-2000-223264, and JP-A-2003-17244). This technology is called a thin-film sealing method. By forming the gas barrier layer using such a technology, the thin film can be formed such that moisture is completely blocked.
The gas barrier layer is made of an inorganic film, which is extremely hard at high density, in order to have moisture blocking property. For this reason, if an uneven portion or a steep step exists at the surface of the thin film, external stress is concentrated, and thus a crack or removal may occur. Accordingly, in order to suppress the crack or removal due to stress, a buffering layer needs to be disposed to come into contact with the gas barrier layer so as to enhance adherence to the gas barrier layer and to realize planarization. As such a buffering layer, it is preferable to use a material having planarization property, flexibility and stress-absorbing property. For example, an organic high-molecular-weight material is suitably used.
However, the inventors has confirmed that, even when the technologies described in the above-described publications are used and the buffering layer is disposed, sufficient light-emitting properties or light-emitting lifetime are not obtained and a non-light-emitting region is generated. In particular, in order to ensure planarization property of the buffering layer, a process of coating the planar buffering layer with no loss is needed, without causing bubbles or the like, since the buffering layer cannot spread out by the weight caused by the contact with the substrate, unlike a bonding adhesive. It is very important for a high-quality gas barrier layer to be provided.